System and method for scanning the depth of the optic fundus

ABSTRACT

A system and method for obtaining a depth profile of the fundus of the eye in which first and second alternately excited light sources image an aperture on a portion of the optic disk. The refractive power of the eye is held approximately constant by having the eye look at a fixation point. A detector is provided for sensing the degree of overlap of the aperture images due to the first and second light sources. In one embodiment the aperture is displaced in a Z-direction with respect to the eye until the images of the aperture completely overlap. The aperture is then successively displaced horizontally in an X-direction and/or vertically in a Y-direction with respect to the eye and in each position the aperture is adjusted in the Z-direction until the first and second images of the aperture completely overlap. The positions of the aperture where the first and second images thereof overlap correspond to the depth of the respective portions of the optic fundus from any arbitrary point at the front of the eye.

l] :1 t: t] rte States i atet {151 3,639,041 Cornsweet 51 Feb. 1, 1972[54] SYSTEM AND METHOD FOR pps. 1636- l639,Nov. I965 SCANNING THE DEPTHOF THE OPTIC Jay Warshawsky, High-Resolution Optometer..., JOSA, FUNDUSvol. 54, no. 3, pps. 375- 379, Mar. 1964 Merrill J. Allen et al., AnInfrared Optometer..., Amer. J. Inventor: Tom Cornsweet, Atherwn, CahfiOptom. & Arch Amer. Acad. Opt., vol. 37, pp. 403- 407, [73] Assignee:Stanford Research Institute, Menlo Park, 1960 Cahf' PrimaryExaminer-David Schonberg [221 Filed: Sept. 21, 1970 AssistantExaminerPaul A. Sacher [2]] p No 73 990 Attorney-Flehr, Hohbach, Test,Albritton and Herbert [57] ABSTRACT [52] us Cl z g gg c A system andmethod for obtaining a depth profile of the fun- [511 Int. CL l A61b00H) 11/30 dolbwoo dus of the eye in which first and second alternatelyexcited [58] Field of's cijflff ..3 5l/6 7 13 1'4 16 39 1- image anaperture 3 of OPiC disk- The refractive power of the eye is heldapproximately constant by having the eye look at a fixation point. Adetector is pro- [56] References Cited vided for sensing the degree ofoverlap of the aperture images due to the first and second lightsources. In one embodiment UNITED STATES PATENTS the aperture isdisplaced in a Zdirection with respect to the eye until the images ofthe aperture completely overlap. The 2 if 7 aperture is thensuccessively displaced horizontally in an X- 3572909 3/1971 g adirection and/or vertically in a Y-direction with respect to the 35655682/197] a X eye and in each position the aperture is adjusted in the Z-0C direction until the first and second images of the aperture OTHERPUBLICATIONS completely overlap. The positions of the aperture where theF. W. Campbell et al., High-Speed Infrared Optometer, JOSA, vol. 49, No.3, pps. 268- 272, Mar. 1959 Niles Roth, Automatic Optometer...UndruggedHuman Eye," The Review of Scientific Instruments, Vol. 36, no. 11,

first and second images thereof overlap correspond to the depth of therespective portions of the optic fundus from any arbitrary point at thefront of the eye.

8 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION Certainpathological conditions are accompanied by a bulging or cupping of theoptic fundus in the vicinity of the optic nerve head in the eye. Forexample, in the case of brain tumors, the normal pressure differentialbetween the interior of the skull and the interior of the eye maychange. This change in pressure differential can cause bulging of theoptic nerve head, or disk into the eye.

Glaucoma is a disorder that is almost invariably accompanied by acupping of the optic disk (a bulging out of the eye). In the caseofglaucoma, the cupping is due to atrophy of thenerve fibers in the eyeand possibly to an increase in the intraocular pressure. It is thereforeapparent that it is desirable to have a method and system for detectingsuch bulging or cupping.

Opthalmoscopes are commonly used to look into a patients eye in anattempt to visually detect bulging or cupping of the optic disk. Suchvisual examinations, however, have not proven to manifest a desirabledegree of reliability or accuracv.

What is needed is a fast and accurate method and system for measuringbulging or cupping of the optic fundus for use in diagnosis ofpathological conditions, especially glaucoma. Such a method and systemmight also be useful for broad screening of a large number of patientssuch as in hospitals, mobile medical units or possibly as a routineprocedure in connection with obtaining a drivers license.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto provide an improved method and system for detecting bulging orcupping of regions of the optic fundus by obtaining a depth profile ofthe optic fundus.

Briefly, in accordance with one embodiment of the invention, an image ofan aperture is formed on the fundus of a patients eye. A fixation pointis provided for the patient to look at in order that the refractivestrength of the eye stays approximately constant. Means are provided forvarying the axial distance between the aperture and the optic fundusuntil the aperture is in sharp focus on the fundus. The image of theaperture is caused to scan across different portions of the fundus; theaxial position of the aperture that produces a sharply focused image onthe fundus is a direct measure of the distance between an arbitrarypoint on the frontof the eye (such as the nodal point, or opticalcenter" ofthe eye and the fundus at the point where the aperture isimaged. Therefore, as the aperture scans across the fundus, thediffering axial distance of the aperture with respect to the fundus fora sharply focused image of the aperture to be produced thereon is adepth profile of the scanned region ofthe optic fundus.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram of an opticfundus depth scanner illustrating the manner in which an aperture may bemoved in .r, y, and 2 directions.

FIG. 2 is a graph of the null position of the aperture in the zdirection versus the position of the aperture in the XY plane for both anormal fundus and one in which there is bulging of the optic disk.

FIG. 3 is similar to FIG. 1 but shows another embodiment of a portion ofan optic fundus depth scanner in which it is not necessary to adjust the2 position of the aperture means for every position of the aperture inthe XY plane.

FIG. 4 shows another embodiment of aperture and detecting means whichutilizes a plurality of apertures and a plurality of photodetectors forsimultaneously scanning a plurality of portions ofthe optic fundus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An automatic optometer measuresthe refractive power of the eye by projecting narrow beams of light atat least two areas of the entrance pupil of the eye, the refractivesurfaces of the eye directing the beams to the retina. The refractiveelements of the eye are primarily the air-to-cornea interface and thevarious interfaces related to the lens within the eye. For generalpurposes, all of these elements may be considered as a single refractiveelement, which will be referred to herein as the eye lens. If the anglesat which the beams strike the eye lens are properly related to thefocusing power of the eye lens, the beam will be directed onto the samearea of the retina i.e., they will completely overlap.

The angles at which the beams enter the eye lens may be controlled byplacing an aperture in the pathof the beams and varying the distancebetween the aperture and the eye lens.

If the relative angles of incidence of the beams and the refractive orfocusing power of the eye lens are not properly related, the images ofthe aperture on the retina will be separated. A determination of whetherthe images on the retina are overlapping or not is made by directinglight passing out of the eye lens through a converging lens which formsan image of the light patterns-that are present on the retina. Therelative angles of incidence of the narrow beams on the eye lens arethen altered by moving the aperture to make the retina images overlapand the angles required to achieve overlapping indicate refractive powerof the eye lens. However, if the refractive strength of the eye does notchange, but the image of the aperture is caused to scan across differentparts of the retina, then the position of the aperture with respect tothe eye lens for the aperture image to be sharply focused on the retinais a direct measure of the distance between an arbitrary point at thefront of the eye (such as nodal point of the eye) and the retina at thepoint where the aperture is imaged. Therefore, if the patient steadilyviews some target at a fixed position in space so that his refractivechanges are small and random and the aperture is made to scan across thepart of the retina that is of interest, with the position of theaperture being adjusted at each point of the scan such that the twoimages of the aperture overlap, the resulting read out of the positionsof the aperture during the scan is a depth profile of the scanned regionof the retina.

Referring to FIG. 1 an eye 11 having a lens 12 and a retina 13 isdisposed at an eye station generally indicated by reference numeral 14.A fixation point or object 16 is provided for the eye 11 to focus on sothat refractive changes in the eye lens 12 will be small and random.Light sources 17 and 18 are provided, which according to one embodimentare alternately excited xenon flash lamps. A lens 19 images the lightsource 17 in an aperture 21 ofa plane 22. A lens 23 and a mirror 24image the light source 18 in an aperture 26 of the plane 22. The lightsources 17 and 18 are adapted to be alternately excited so that theapertures 21 and 26 of the plane 22 are alternately illuminated. Lightpassing through apertures 21 and 26 is collimated by a lens 27. Thecollimated light passing through the lens 27 is incident on a plane 28.The plane 28 has an aperture '29 which passes a portion of thecollimated light from the lens 27. A lens 31 and a beamsplitter 32(which may, for example, be a half-silvered mirror) are situated betweenthe plane 28 and the eye station 14. The lens 31 images the light fromthe light sources 17 and 18 (and apertures 21 and 26) through the beamsplitter 32 onto the plane of the eye lens 12. Thus only a very narrowbeam of light proportional to the area of the semicircular area 21 or 26passes through the eye lens 12 at any instant.

The aperture 29 is adapted to be imaged by the lens 31 and the eye lens12 on the retina 13 of the eye 11. If the plane 28 is located in the zdirection (as shown by the rectangular .r, y, and z coordinance inFIG. 1) .with respect to the lens 31 and the eye lens 12 such that theimage of the aperture 29 is sharply focused on the retina 13, the imagewill not move as the lightv sources 17 and 18 are alternated. However,if the plane 28 is not conjugate with the retina 13, then the image ofthe aperture 29 will shift back and forth on the retina 13 as the lightsources 17 and 18 are alternated due to the distance d which separatethe semicircular apertures 21 and 26 in the plane 22. Thus a compositeimage is formed on the retina 13 as the light sources 17 and 18alternate which is comprised of a first image ofthe aperture 29 due tothe light source 17 and a second image of the aperture 29 due to thelight source 18. With any given refractive power of the eye lens 12 theimages of the aperture 29 on the retina 13 as the light sources 17 and18 are alternated may be sharply focused such that they completelyoverlap by displacing the plane 28 in the z direction until the aperture29 is conjugate with the retina 13.

Detecting means is provided for sensing the sharpness of focus of thecomposite image of aperture 29 on the retina 13; that is, the degree ofoverlap of the two images of the aperture 29. The beam splitter 32 isadapted to reflect the composite image on retina 13 through a lens 33 toa mirror 34 which in turn reflects the composite image to aphotodetector 36. The photodetector 36 comprises an arrangement forsensing the distribution of light falling thereon and may convenientlybe a split field photodetector having fields 36a and 36b. Photodetectingmeans having more than two fields may obviously be substituted for thesplit field photodetector 36. Conductors 37 and 38 connect the fields36a and 36b respectively to a subtractor and null detector 39. If theaperture 29 is sharply focused on the retina 13 then its image does notmove as the light sources 17 and 18 are alternated. In this case thelight sensed by the two photodetector fields 36a and 36!) will not varyas the light sources are alternated (the intensities of the two sourcesare equated before operating). The subtractor and null detector 39subtracts the electrical outputs of the two fields 36a and 36b which arepresent on conductors 37 and 38 and detects an AC null of the differencebetween them.

As illustrated in FIG. 1, both the photodetector 36 and the plane 28having the aperture 29 therein are affixed to an adjustable member 41.The adjustable member 41 is connected through an arm 42 to a servo 43.The servo 43 receives the output ofthe subtractor and null detector 39as an input and is responsive thereto to adjust the adjustable member 41back and forth along the z direction until there is a null output fromthe subtractor and null detector 39. The servo 43 is adapted to sensewhich direction along the z axis to shift the plane 28 by comparing thephase of signals from the photodetector 36 with the phase of thealternation of light sources 17 and 18. When there is such a null outputthe aperture 29 is sharply focused on the retina 13. The position of theplane 28 for the null in the z direction is then recorded. As shown inFIG. 1 an XY positioner 45 is provided and is adapted to selectivelymove the adjustable member 41 and hence the aperture 29 to variouspoints in the XY plane. The position of the aperture 29 with respect tothe eye 11 is thus successively moved to new points in the XY plane. Ateach of these new points the servo 43 adjusts the adjustable member 41in the z direction and hence the aperture 29 until it is sharply focusedon the retina 13 so that a null output is detected on the output ofthesubtractor and null detector 39. This null position of the plane 28 inthe z direction is also then recorded. The adjustable member 41 is thendisplaced to a new position in the XY plane and is adjusted by servo 43until the aperture 29 is again sharply focused on the retina 13. Thisposition in the z direction is also then recorded. This procedure isrepeated for as many points in the XY plane as desired. In this manner adepth profile of the retina 13 showing the depth of the retina 13 froman arbitrary point at the front of the eye is obtained. That is, as theposition of the aperture 29 shifts in the XY plane the composite imagethereof formed on the retina 13 is formed on different portions oftheretina 13. With the refractive power of the eye 11 held constant byhaving it look at the fixation point 16, the position of the aperture 29in the z direction for the composite image thereof to be sharply focusedon the retina 13 is proportional to the distance between the portion ofthe retina on which the composite image of the aperture 29 falls and anarbitrary point toward the front of the eye, such as the nodal point ofthe eye. Thus, referring to FIG. 2, there is shown a graph in which thenull position of the aperture 29 in the z direction is plotted againstthe position (say along the direction) of aperture 29 in the XY plane.For a normal eye in which there is little bulging or cupping ofthe opticdisk a curve illustrated by the solid line 44 results which is acontinuous curve proportional to the depth of the scanned portions oftheretina from an arbitrary point at the front of the eye. However, ifthere is any bulging or cupping of the optic nerve head, a curve such asthe dotted curve 46 in FIG. 2 will result. The bulging or cupping isreflected in a bulging or cupping ofthe curve 46. (The dashed curve inFIG. 2 represents what would be called bulging, while a bulge upward inthe figure would ordinarily be called cupping.)

FIG. 3 shows another embodiment of the invention in which it is notnecessary to adjust the adjustable member 41 in the z direction for eachposition in the XY plane. In FIG. 3 only the adjustable member 41 withthe photodetector 36 and plane 28 is shown. The lenses, light sourcesand mirrors for the embodiment shown in FIG. 3 are the same as inFIG. 1. In FIG. 3 the adjustable member 41 is, as before, connectedthrough the member 42 to an XY positioner 45 which is adapted to movethe adjustable member 41 and hence the plane 28 and aperture 29 tovarious points in the XY plane. The split field photodetector 36 havingfields 36a and 36b is connected via conductors 37 and 38 to a subtractor39. The conductors 37 and 38 also form the input to a summer 48. Theoutput of the subtractor 39 is connected to a multiplier 51. Themultiplier 51 also receives the output of summer 48 as an input. Theoutput of multiplier 51 drives a chart recorder 52.

In operation, the position of the adjustable member 41 and hence theaperture 29 in the z direction is adjusted (the adjustment may be manualor servo-controlled until the aperture 29 is sharply focused on aportion of the retina so that the output of the subtractor 39 is anonvarying quantity; that is, it has no AC components. The output ofsubtractor 39 also forms an input to the multiplier 51. Another input tothe multiplier 51 is the output of the summer 48. This sum isproportional to the total amount of light falling on the photodetector.Multiplier 51 multiplies the output of the subtractor 39 with the sum ofthe outputs of the two fields 36a and 36b ofthe photodetector. Thus, theAC output of the multiplier 51 as the aperture 29 is displaced in the XYplane is proportional to the amount by which the composite image of theaperture 29 is defocused on the portions of the retina that are beingscanned. This directly indicates the depths of these portions of theretina with respect to an arbitrary point at the front ofthe eye as theaperture 29 is moved in the XY plane. The output of the multiplier 51can be recorded, for example, on a chart recorder 52 which will yield adepth profile similar to that shown in FIG. 2. An examination of thisdepth profile will reveal any bulging or cupping of the optic fundus.

The purpose of the multiplier 51 is to correct for possible sources oferror. The distance through which the image of the aperture 29 shifts asthe light sources 17 and 18 are alternated is directly proportional tothe depth of the fundus at the point where the image falls. However, theamounts of light falling on the photodetector fields is measured ratherthan the displacement ofthe images. If everything were perfectlyconstant, then those amounts of light would be linear with the shifts inposition of the images and the AC component of the difference betweenthe amounts of light would be an accurate indication of the depth of thefundus. If the light intensity falling on the photodetector fieldschanges for any reason than the outputs of the photodetector fieldschanges, thus giving false depth indications. The light intensity canchange for a number of reasons, such as the lamps themselves changing,the pupil of the patients eye changing its diameter, or the imagesfalling on regions of the retina whose reflection characteristics aredifferent. To compensate for these possible sources of error, it isnecessary to measure the actual intensity of light and correct for anychanges in it. The sum signal from summer 48 is a measure of the totalintensity of the light and therefore, when it is properly introduced asa multiplying factor, it corrects for changes in the intensity of thelight. It should be noted, however, that errors due to changes in lightintensity are not present when the AC output is nulled at each positionin the XY plane by displacing the aperture 29 in the z direction as inthe other embodiments herein. The null is unaffected by changes in thelight intensity.

Of course, instead of moving the aperture 29 in the XY plane so that thedepth profile of the retina is obtained sequentially it is possible toprovide a plurality of apertures and a plurality of photodetectors suchthat all measurements are made simultaneously. Thus, referring to FIG.4, a support member 53 supports a plane 54 which has a plurality ofapertures 56 therein. The support member 53 also supports a member 57which has a plurality of split-field photodetectors 58 arranged in thesame respective orientation as are the apertures 56. Each of thephotodetectors 58 requires electronics such as shown in the embodimentof FIG. 3 which include a subtractor, a summer, and a multiplier.Alternately one set of electronics can be provided with the outputs ofthe photodetectors 58 sequentially applied to the electronics.

In operation, with the arrangement shown in FIG. 4, the position of theplane 54 is adjusted in the z direction until the aperture 56a issharply focused on a portion of the retina such that the differencebetween the two fields of the split field photo detector 58a contains noAC components. The AC outputs from the difference between the twosignals on the split fields of each of the other photodetectors 58 ismultiplied by the sum of the signals generated by the two split fieldsof each of the respective photodetectors. These varioussignals are thenrepresentative of the depths of the various portions of the retina onwhich the composite images of the apertures 56 fall with respect to anarbitrary point at the front of the eye. The signals can be applied to achart recorder as was done in connection with the embodiment of PK]. 3to generate a graph such as that shown in HO. 2 in which bulging orcupping of the optic nerve head is indicated by the bulging or cuppingof a curve generated by the chart recorder.

Thus what has been described is an improved method and system forscanning a retina in order to detect bulging or cupping of the opticfundus. This is done by obtaining a depth profile of the fundus which isachieved by projecting light images into the eye and sensing the imagesthat are formed on the fundus. Although the invention has been describedwith respect to specific embodiments thereof it should be obvious tothose skilled in the art that minor modifications and changes may bemade to the embodiments disclosed herein without departing from the truespirit and scope of the invennon.

We claim:

1. An optic fundus depth scanner for use with an eye having an opticfundus and a lens and adapted to scan the fundus thereof comprising aneye station for establishing the position of the eye with respect to x,y, and 2 directions, fixation means for the eye to look at whereby therefractive power of the eye is approximately constant, light means forprojecting light in first and second predetermined optical pathsgenerally in the z direction, plane means spaced from said light meansin the z direction and having aperture means for passing portions ofprojected light from said light means therethrough, lens meanspositioned between said plane means and said eye station in the zdirection for forming an image of said light means on the eye lenswhereby light passes through the eye lens and falls on portions of theoptic fundus to form composite images of said aperture means thereon,detecting means for detecting the sharpness of focus of said compositeimages of said aperture means on said portions of the optic fundus,means for successively displacing said plane means in the XY planeformed by the x and y directions whereby the composite image of saidaperture falls on successive other portions of the optic fundus, andindicating means coupled to said detecting means and responsive to thesharpness of focus of said composite images of said aperture means onthe portions of the optic fundus to indicate the relative respectivedistances between the portions of the optic fundus and the eye lenswhereby a profile of the optic fundus is obtained.

2. The optic fundus depth scanner of claim ll wherein said detectingmeans comprises a split field photodetector having first and secondfields, optical means for coupling said split field photodetectorgenerates electrical signals indicative of the sharpness of focus ofsaid composite image of said aperture means on the portion ofthe opticfundus.

3. The optic fundus depth scanner of claim 1 wherein said aperture meanscomprises a plurality of apertures spaced from one another in the XYplane and wherein said detecting means comprises a plurality ofphotodetectors spaced from one another in the XY plane for respectivelydetecting the sharpness of focus of said composite images of each ofsaid apertures.

4. A method of scanning the optic fundus of an eye having an opticfundus and a lens comprising the steps of establishing the position ofthe eye at an eye station with respect to y, and 1 directions, providinga fixation point for the eye to look at whereby the refractive power ofthe eye is approximately constant, projecting light in first and secondpredetermined optical paths generally in the z direction, passing aportion of the projected light through an aperture in a plane, imagingthe portion of projected light on the eye lens whereby an image of theaperture is formed on the portion of the optic fundus, displacing theplane in the z direction until the aperture is sharply focused on theportion of the optic funds whereby the position of the plane means inthe z direction corresponds to the distance of the portion of the opticfunds from the eye lens, displacing the plane successively to aplurality of positions in the XY plane formed by the x and y directionswhereby images of the aperture are successively formed on a plurality ofportions of the optic fundus, displacing the plane in the z directionfor each of the positions in the XY plane until the aperture is sharplyfocused on the respective portions of the optic fundus whereby thesuccessive positions of the plane means in the z direction correspond tothe distance of the respective portions of the optic fundus from the eyelens.

5. An optic fundus depth scanner for use with an eye having an opticfundus and a lens and adapted to scan the fundus thereof comprising aneye station for establishing the position of the eye with respect to y,and z directions, fixation means for the eye to look at whereby therefractive power of the eye is approximately constant, light means forprojecting light in first and second predetermined optical pathsgenerally in the z direction, a first lens spaced from said light meansin the z direction for collimating said light from said light means,plane means spaced from said first lens in the z direction and having anaperture for passing a portion of collimated light from said first lenstherethrough, a second lens positioned between said plane means and saideye station in the z direction for forming an image of said light meanson the eye lens whereby light passes through the eye lens and falls on aportion of the optic fundus to form a composite image of said aperturethereon, detecting means for detecting sharpness of focus of saidcomposite image of said aperture on said portion of the optic fundus,means for displacing said plane means in the z direction until saiddetecting means indicates that said composite image of said aperture issharply focused on said portion of the optic fundus whereby the positionof said plane means in the z direction corresponds to the distance ofsaid portion of the optic fundus from the eye lens, means forsuccessively displacing said plane means in the XY plane formed by the xand y directions whereby the composite image of said aperture falls onsuccessive other portions of the optic fundus, and indicating meanscoupled to said detecting means and responsive to the sharpness of focusof said composite image of said aperture on the successive otherportions of the optic fundus to indicate the respective distancesbetween the successive other portions of the optic fundus and the eyelens.

6. The optic fundus depth scanner of claim wherein said indicating meanscomprises means for displacing said plane means in the z direction ateach successive position of said plane means in the XY plane until saiddetecting means indicates that said composite image of said aperture foreach of 5 the successive positions of the plane means in the XY plane issharply focused on the respective other portion of the optic fundus.

7. The optic fundus depth scanner of claim 3 wherein said light meanscomprises first and second light sources which are alternately excitedto alternately project light along said respective first and secondpredetermined optical paths whereby images of said first and secondlight sources are formed on first and second portions of the eye lensand first and second images of said aperture form said composite imageon a portion of the optic fundus, the sharpness of focus of saidcomposite image determined by the amount of overlap of said first andsecond images of said aperture, and wherein said detecting meanscomprises a split field photodetector having first and second fields andoptical means for coupling said split field photodetector to said eyestation whereby said split field photodetector generates electricalsignals indicative of the sharpness of focus of said composite image ofsaid aperture on the portion of the optic fundus.

8. The optic fundus depth scanner of claim 7 wherein said indicatingmeans comprises means for calculating the difference between the amountsoflight falling on said respective first and second fields of said splitfield photodetector and generating a difference signal for each positionof said aperture in the XY plane, means for summing the amounts oflightfalling on said respective first and second fields of said split fieldphotodetector and generating a sum signal for each position of saidaperture in the XY plane, and means for multiplying said differencesignal with said sum signal for each position ofsaid aperture in the XYplane to form an output, said output being proportional to therespective distance between the portion of the optic fundus upon whichsaid aperture is imaged for each position of said aperture in the XYplane and the eye lens whereby a depth profile of the optic fundus isobtained.

1. An optic fundus depth scanner for use with an eye having an opticfundus and a lens and adapted to scan the fundus thereof comprising aneye station for establishing the position of the eye with respect to x,y, and z directions, fixation means for the eye to look at whereby therefractive power of the eye is approximately constant, light means forprojecting light in first and second predetermined optical pathsgenerally in the z direction, plane means spaced from said light meansin the z direction and having aperture means for passing portions ofprojected light from said light means therethrough, lens meanspositioned between said plane means and said eye station in the zdirection for forming an image of said light means on the eye lenswhereby light passes through the eye lens and falls on portions of theoptic fundus to form composite images of said aperture means thereon,detecting means for detecting the sharpness of focus of said compositeimages of said aperture means on said portions of the optic fundus,means for successively displacing said plane means in the XY planeformed by the x and y directions whereby the composite image of saidaperture falls on successive other portions of the optic fundus, andindicating means coupled to said detecting means and responsive to thesharpness of focus of said composite images of said aperture means onthe portions of the optic fundus to indicate the relative respectivedistances between the portions of the optic fundus and the eye lenswhereby a profile of the Optic fundus is obtained.
 2. The optic fundusdepth scanner of claim 1 wherein said detecting means comprises a splitfield photodetector having first and second fields, optical means forcoupling said split field photodetector generates electrical signalsindicative of the sharpness of focus of said composite image of saidaperture means on the portion of the optic fundus.
 3. The optic fundusdepth scanner of claim 1 wherein said aperture means comprises aplurality of apertures spaced from one another in the XY plane andwherein said detecting means comprises a plurality of photodetectorsspaced from one another in the XY plane for respectively detecting thesharpness of focus of said composite images of each of said apertures.4. A method of scanning the optic fundus of an eye having an opticfundus and a lens comprising the steps of establishing the position ofthe eye at an eye station with respect to x, y, and z directions,providing a fixation point for the eye to look at whereby the refractivepower of the eye is approximately constant, projecting light in firstand second predetermined optical paths generally in the z direction,passing a portion of the projected light through an aperture in a plane,imaging the portion of projected light on the eye lens whereby an imageof the aperture is formed on the portion of the optic fundus, displacingthe plane in the z direction until the aperture is sharply focused onthe portion of the optic funds whereby the position of the plane meansin the z direction corresponds to the distance of the portion of theoptic funds from the eye lens, displacing the plane successively to aplurality of positions in the XY plane formed by the x and y directionswhereby images of the aperture are successively formed on a plurality ofportions of the optic fundus, displacing the plane in the z directionfor each of the positions in the XY plane until the aperture is sharplyfocused on the respective portions of the optic fundus whereby thesuccessive positions of the plane means in the z direction correspond tothe distance of the respective portions of the optic fundus from the eyelens.
 5. An optic fundus depth scanner for use with an eye having anoptic fundus and a lens and adapted to scan the fundus thereofcomprising an eye station for establishing the position of the eye withrespect to x, y, and z directions, fixation means for the eye to look atwhereby the refractive power of the eye is approximately constant, lightmeans for projecting light in first and second predetermined opticalpaths generally in the z direction, a first lens spaced from said lightmeans in the z direction for collimating said light from said lightmeans, plane means spaced from said first lens in the z direction andhaving an aperture for passing a portion of collimated light from saidfirst lens therethrough, a second lens positioned between said planemeans and said eye station in the z direction for forming an image ofsaid light means on the eye lens whereby light passes through the eyelens and falls on a portion of the optic fundus to form a compositeimage of said aperture thereon, detecting means for detecting sharpnessof focus of said composite image of said aperture on said portion of theoptic fundus, means for displacing said plane means in the z directionuntil said detecting means indicates that said composite image of saidaperture is sharply focused on said portion of the optic fundus wherebythe position of said plane means in the z direction corresponds to thedistance of said portion of the optic fundus from the eye lens, meansfor successively displacing said plane means in the XY plane formed bythe x and y directions whereby the composite image of said aperturefalls on successive other portions of the optic fundus, and indicatingmeans coupled to said detecting means and responsive to the sharpness offocus of said composite image of said aperture on the successive otherportions of the optic fundus to indicate the respective distancesbetween the successive other portions of the optic fundus and the eyelens.
 6. The optic fundus depth scanner of claim 5 wherein saidindicating means comprises means for displacing said plane means in thez direction at each successive position of said plane means in the XYplane until said detecting means indicates that said composite image ofsaid aperture for each of the successive positions of the plane means inthe XY plane is sharply focused on the respective other portion of theoptic fundus.
 7. The optic fundus depth scanner of claim 3 wherein saidlight means comprises first and second light sources which arealternately excited to alternately project light along said respectivefirst and second predetermined optical paths whereby images of saidfirst and second light sources are formed on first and second portionsof the eye lens and first and second images of said aperture form saidcomposite image on a portion of the optic fundus, the sharpness of focusof said composite image determined by the amount of overlap of saidfirst and second images of said aperture, and wherein said detectingmeans comprises a split field photodetector having first and secondfields and optical means for coupling said split field photodetector tosaid eye station whereby said split field photodetector generateselectrical signals indicative of the sharpness of focus of saidcomposite image of said aperture on the portion of the optic fundus. 8.The optic fundus depth scanner of claim 7 wherein said indicating meanscomprises means for calculating the difference between the amounts oflight falling on said respective first and second fields of said splitfield photodetector and generating a difference signal for each positionof said aperture in the XY plane, means for summing the amounts of lightfalling on said respective first and second fields of said split fieldphotodetector and generating a sum signal for each position of saidaperture in the XY plane, and means for multiplying said differencesignal with said sum signal for each position of said aperture in the XYplane to form an output, said output being proportional to therespective distance between the portion of the optic fundus upon whichsaid aperture is imaged for each position of said aperture in the XYplane and the eye lens whereby a depth profile of the optic fundus isobtained.